Aromatic Thiones Research Articles

Radiationless decay of aromatic thiones in solution selectively excited to their S3, S2, S1, and T1 states

Etude du declin sans radiation de thiones aromatiques sous l'excitation selective de leurs etats singulets-1,2,3 et triplet 1

T 1–T 2 inversion in aromatic thiones

The emission spectra and phosphorescence lifetimes and quantum yields, of xanthione (XT), 4H-pyran-4-thione (PT) and 4H-1-benzopyran-4-thione (BPT) have been measured in five solvents of varying polarities at room temperature. A dramatic change in the T 1→S 0 phosphorescence spectrum is observed, and this is interpreted in terms of inversion of the 3(n, π*) and 3(π,π*) states with increasing solvent polarity. Only modest variations in the radiative and non-radiative decay constants for the triplet are observed, and no evidence of bi-exponential decay is found. Strong coupling between T 1-T 2 and between the singlet and triplet manifolds is indicated. Comparisons are drawn with ketones of similar structure.

A laser flash photolysis study of pivalothiophenone triplets: steric and electronic effects in thione photoreaction kinetics

Upon laser pulse excitation (Aex = 532 nm) into the lowest-lying '(n,a*) band system, pivalothiophenones in benzene solutions give rise to short-lived triplets (Ama: = 325-335 nm, em: = (1 1-15) X lo3 M-' cm-I) with quantitative intersystem crossing efficiencies. The triplet yields decrease slightly (by 10-30%) upon changing A, to 308 nm (Le., upon excitation into S2). Kinetic data are presented for intrinsic triplet lifetimes, self-quenching, and quenching by oxygen, di-tert-butylnitroxy radical, and various reagents capable of interacting with the triplets via energy, electron, or hydrogen-atom transfer and by biradical formation (possibly leading to cycloaddition). The mechanisms of the quenching processes are discussed. Relative to rigid aromatic thiones, namely, xanthione and thiocoumarin, the interaction of pivalothiophenone triplets with most of the quenchers are kinetically inefficient. This is interpreted primarily as a manifestation of the steric crowding at positions a to the thiocarbonyl group.

ChemInform Abstract: An Extremely Short‐Lived 1,4‐Biradical as Intermediate in the Photocycloaddition Reactions of Triplet State Aromatic Thiones with Allenes.

AbstractThe question is studied as to whether an exciplex or a 1,4‐biradical or both appear as intermediates in the photochemical reaction of aromatic thiones (I) and (II) with allenes such as (III)‐(V) and (IX), the butatriene (VII), or acetylenes (VI).

Thermally activated delayed S1 fluorescence of aromatic thiones

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThermally activated delayed S1 fluorescence of aromatic thionesAndrzej Maciejewski, Marian Szymanski, and Ronald P. SteerCite this: J. Phys. Chem. 1986, 90, 23, 6314–6318Publication Date (Print):November 1, 1986Publication History Published online1 May 2002Published inissue 1 November 1986https://doi.org/10.1021/j100281a051RIGHTS & PERMISSIONSArticle Views704Altmetric-Citations66LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (586 KB) Get e-Alerts

Thermal cycloaddition reaction of xanthene‐9‐thione with allenes: An ESR study

AbstractDuring the parallel (2 + 2)‐ and (4 + 2)‐cycloaddition reactions of aromatic thiones such as xanthene‐9‐thione with substituted allenes XCHCCH2 (X = OR, SR, NMe2, Ph), a strong ESR signal is observed. This signal is associated with the (4 + 2)‐cycloaddition reaction, affording thiopyran derivatives 3,11b‐dihydro‐2‐(X‐methylene)‐2H‐thiopyrano[4,3,2‐kl]xanthene F or 3,11b‐dihydro‐3X‐2‐methylene‐2H‐thiopyrano[4,3,2‐kl]xanthene E. Computer analyses of this signal made possible its identification as emanating from a 9‐xanthenyl radical substituted at the 1‐ and 9‐positions. The type of xanthenyl radical that is formed in the thermal reaction E rad or F rad depends on the nature of the substituent X at the allenic system H2CCCHX. This investigation shows that where X = Ph and NMe2, xanthenyl radicals of structure E rad are produced, and where X = O‐t‐Bu and S‐t‐Bu xanthenyl radicals of structure F rad are produced. It is striking that this production is so selective.On irradiation (λ>254nm), the production of xanthenyl radicals is enhanced. The conformation of xanthenyl radicals E rad and the role of E rad and F rad in the formation of addition products E and F are discussed.

An extremely short-lived 1,4-biradical as intermediate in the photo-cycloaddition reactions of triplet state aromatic thiones with allenes

The photochemical reaction of xanthene-9-thione, thiobenzophenones, and thioxanthene-9-thione with allenes has been studied by initiating the reaction with a 308 nm laser flash and by following transient u.v.–visible optical absorptions on a nanosecond time scale. In the wavelength range 320 < λ < 800 nm there is only a transient absorption arising from the thione in its lowest triplet state T1(nπ*). The rate constant ka for quenching of the thione in this state by allenes is determined from Stern–Volmer plots. A 1,4-biradical which appears as a reaction intermediate could be scavenged with NN′-dimethyl-4,4′-bipyridinium dichloride (methyl viologen, MV). The yield of the methyl viologen radical cation MVRC resulting from scavenging has been determined as a function of the concentration of MV. A lifetime of 90 ps follows from this for the 1,4-biradical (8). The short lifetime is attributed to a large spin density on the sulphur atom from both unpaired electrons, causing efficient local spin–orbit coupling. Both the logarithm of the rate constant kt for the disappearance of the aromatic thione in the thermal reaction with an allene and log ka depend linearly on the ionization energy of the allene. Previous suggestions that the 1,4-biradical has a triplet state exciplex as precursor are rejected on the basis of the similarity of these relations and because of the fact that there is no difference in the effect on ka and kt caused by deuteriation of the allene.

Relaxation of the second excited singlet states of aromatic thiones: the role of specific solute-solvent interactions

Relaxation of the second excited singlet states of aromatic thiones: the role of specific solute-solvent interactions

Cycloaddition Reactions of Substituted Allenes with Triplet Excited Aromatic Thiones: Product Formation and Reaction Mechanism

AbstractThe reactivity of substituted allenes H2CCC(R)X towards three triplet aromatic thiones has been investigated. Product analysis reveal the formation of two (2+2)‐cycloaddition products the thietanes 3, 4 (E + Z) and occasionally of one (4+2)‐cycloaddition product, thiopyran derivative (Z)‐5, generally in high overall yields. Steady state measurements show that electron donating substituents in the allenic system enhance the overall reaction rate. There is little effect of solvent polarity on the reaction rate. The correlation between the relative reaction rates and the first adiabatic ionization energy of the substituted allenes is in accordance with the formation of an exciplex between the excited thione and that π‐bond of the allenic system which is conjugated with the substituent X. From this exciplex two isomeric allylic 1,4‐biradicals (Z)‐8 and (E)‐8 are probably formed. After inter‐system crossing, ring closure gives the thietanes 3, (E)‐4, (Z)‐4 and/or thiopyran derivative (Z)‐5. The ratio in which 3, (E)‐4, (Z)‐4 and (Z)‐5 are formed is explained by considering electronic and steric factors in the proposed reaction mechanism. Experiments with an optically active allene (+)‐PhC(H)CC(H)Me support the intermediacy of a non‐chiral relatively stable allylic 1,4‐biradical. At infinite allene concentration the quantum yield approaches 1, indicating no energy loss during the reaction. Thus no measurable disproportionation of the allylic biradicals (Z)‐8 and (E)‐8 occurs.

Radiationless decay of the second excited singlet states of aromatic thiones: Experimental verification of the energy gap law

Abstract S2 → S0 fluorescence quantum yields and S2 lifetimes of eight aromatic thiones in inert perfluoroalkane solutions at room temperature have been measured using picosecond laser techniques. Photostable, structurally rigid thiones undergo S2 → S1 internal conversion at rates consistent with the energy gap law of radiationless transitions. An average electronic coupling matrix element of 1.9 × 102 cm−1 is found.

Photochemical reaction of some aromatic thiones with aryl‐ and alkyl‐substituted (methylthio)acetylenes. The (2+2)‐cycloaddition products and the occurrence of the equilibrium thiete ⇋ α, β‐unsaturated thioxo compound

AbstractUpon irradiation (λ &gt; 525 nm), xanthenethione 2o and thioxanthenethione 2s react in a non‐regiospecific manner with the triple bond of the acetylenes 6a (Ph‐C≡C‐SCH3) and 6b [(2‐thienyl)–C≡C‐SCH3] to produce in each case the two possible (2 + 2)‐cycloaddition products, which were isolated as thietes or α,β‐unsaturated thioxo compounds. In a solution of each of these reaction products, spectroscopic results confirmed the occurrence of the equilibrium thiete ⇋ α, β‐unsaturated thioxo compound. With acetylene 6c (t‐Bu‐C≡C‐SCH3), the photochemically excited thiones 2o and 2s gave, in each case, only the (2 + 2)‐cycloaddition product 8. In solution these thietes 8 do not equilibrate with the corresponding α, β‐unsaturated thiones. Surprisingly, no products could be isolated or detected after irradiation of thiobenzophenone 2h in the presence of acetylenes 6a or 6b.

THE [4 + 2]CYCLOADDITION REACTIONS OF AROMATIC THIONES WITH MALEIC ANHYDRIDE, NORBORNENE, AND NORBORNADIENE

Abstract The reactions of aryl 1-naphthyl thiones and aryl 2-naphthyl thiones with maleic anhydride, norbornene, and norbornadiene gave the 1,4-cycloadducts containing 3,4-dihydro-2 H-thiopyran rings. 7H-Benz[de]anthracene-7-thione also reacted with norbornene and norbornadiene to give similar 1,4-cycloadducts. In the reaction of aryl phenyl thiones with norbornene, initially formed cycloadducts rearranged to aromatized compounds. In these reactions, the aromatic thiones reacted with the olefins as a heterodiene system.

Decay dynamics of aromatic thione triplet states in fluid solution

Phosphorescence emission and excitation spectra, quantum yields, and lifetimes of several aromatic thiones have been measured in fluid solution at room temperature. Excitation to any of the excited electronic states accessible in the near-uv and visible regions of the spectrum results in population of the lowest triplet state with near unit quantum yield. Triplets of relatively inflexible thiones decay non-radiatively with rate constants of the order of 105 s−1 whereas thiones capable of higher amplitude flexion or group rotation exhibit non-radiative decay constants ≥ 107 s−1 at infinite dilution in aprotic solvents. Self-quenching occurs at diffusion-controlled rates.

Photochemical reactions of some aromatic thiones with bis(methylthio)ethyne; (4 + 2)‐ versus (2 + 2)‐cycloaddition products. Spectroscopic evidence for the equilibrium thiete ⇄ α,β‐unsaturated dithioester

AbstractIrradiation (λ &gt; 525 nm) of the aromatic thiones 2 in the presence of bis(methylthio)ethyne 3 causes two cycloaddition reactions to occur between the photochemically excited thione 2 and the acetylene 3, as concluded from the isolated products. Compounds with structure 6 are believed to be products of a (4 + 2)‐cycloaddition reaction, whereas the formation of the isolated α,β‐unsaturated dithio esters 4 is rationalised on the basis of a (2 + 2)‐cycloaddition reaction. The preference for one reaction pathway over the other depends on the thione used and is discussed in terms of the structure of the thione 2. Spectroscopic observation of the equilibrium thiete 5 ⇌ α,β‐unsaturated dithio ester 4, in solution provides direct evidence for the (2 + 2)‐photocycloadducts, thietes 5.

Photochemical reactions of some aromatic thiones with bis(tert‐butylthio)ethyne. Isolation and properties of thietes, the photochemical (2 + 2)‐cycloadducts and their isomeric α,β‐unsaturated dithioesters

AbstractPhotochemical reaction of some aromatic thiones 2 with bis(tert‐butylthio)ethyne 1 affords the α,β‐unsaturated dithio esters 4 via a (2 + 2)‐cycloaddition reaction of the triplet‐excited thiones 2 with acetylene 1. In one case, a (2 + 2)‐cycloadduct, thiete 3o, was isolated. Spectroscopic investigations revealed that in solution there is an equilibrium between this thiete 3o and the isomeric α,β‐unsaturated dithio ester 4o. The generality of this equilibrium phenomenom is examined and discussed with respect to the substituents of the C=C‐C=S moiety of the α,β‐unsaturated dithio esters 4.

Photochemical reactions of some aromatic thiones with bis(methylthio)ethyne; (4 + 2)‐ versus (2 + 2)‐cycloaddition products. Spectroscopic evidence for the equilibrium thiete ⇄ α,β‐unsaturated dithioester

AbstractIrradiation (λ &gt; 525 nm) of the aromatic thiones 2 in the presence of bis(methylthio)‐ethyne 3 causes two cycloaddition reactions to occur between the photochemically excited thione 2 and the acetylene 3, as concluded from the isolated products. Compounds with structure 6 are believed to be products of a (4 + 2)‐cycloaddition reaction, whereas the formation of the isolated α,β‐unsaturated dithio esters 4 is rationalised on the basis of a (2 + 2)‐cycloaddition reaction. The preference for one reaction pathway over the other depends on the thione used and is discussed in terms of the structure of the thione 2. Spectroscopic observation of the equilibrium thiete 5 ⇄ α,β‐unsaturated dithio ester 4, in solution provides direct evidence for the (2 + 2)‐photocycloadducts, thietes 5.

Thione Photochemistry: The Peri Cyclization of some Polycyclic Aromatic Thiones

A number of polycyclic aromatic thiones have been prepared from the corresponding ketones. Several of the thiones in which there is a free peri position cyclize, on excitation in the π* ← n band, to give thiophene derivatives. The structures of these were proven by application of physical methods and by desulfurization to the corresponding benzyl derivatives. The formal hydrogen 1,3 migration involved was, in one case, shown to be intermolecular by the incorporation of deuterium, from deuterium oxide, during the irradiation. In the case of the α-naphthyl derivative, the mechanism of the reaction has been investigated and it has been concluded that the n,π* singlet is the responsible entity.

Reactions of thioketones. Part III. Reaction of chloramine T with aliphatic and aromatic thioketones

Chloramine T reacted readily with aliphatic and aromatic thiones, acting as a nucleophilic and as an oxidizing reagent. The non-thioenolizable thiones, thioadamantanone and thiobenzophenone afforded thio-ozonide products. Thiocamphor, however, gave an unsaturated disulphide dimer which on heating underwent a stereospecific Cope-type rearrangement.

Polarography of thioketones

Aliphatic and aromatic thiones are reduced at the dropping mercury electrode at potentials well below those of the corresponding ketones. The reductions take place by a mechanism whereby an electron is added to the molecule before protonation. The reducibility of camphorthione adds the isolated C=S group to the list of polarographically reducible functions. The half-wave potentials in acetonitrile correlate linearly with n → π* transitions in the electronic spectra.